1. In a bowl, whisk together the milk, oil, flour and egg yolks. Divide into two portions and add cocoa powder to the second portion.
2. In another bowl, beat the egg whites with salt, lemon juice and sugar.
3. Divide the white and dark mixtures into two portions.
4. Transfer to baking sheet, add dark mixture, top with white mixture and sprinkle with chocolate chips.
5. Bake with hot water at 170°C (340°F) for 1 hour.
